Testing wireless devices for electromagnetic compatibility

by Nicholas Abbondante, Chief Engineer for EMC, Intertek Group

Wireless devices must function in an increasingly hostile RF environment. Here are a few tips on setting up a test regime that can uncover problems.

It is increasingly critical to test and evaluate wireless devices for electromagnetic interference (EMI) and to ensure they comply with electromagnetic compatibility (EMC) rules. EMI can cause minor problems (a blip on a monitor; an accidental alarm that is ultimately no cause for concern) or more serious issues. In medical devices, for example, EMI can interfere with a pacemaker or interrupt a ventilator. Testing and evaluation to mitigate EMI and ensure EMC compliance helps designers make sure new devices pose minimal risk of failing or interfering with other devices in the area.

Government regulating bodies, such as the Federal Food and Drug Administration, require certain products under their purview be tested for EMC compliance before being sold commercially. Manufacturers may run EMC tests themselves or do so through third-party organizations. Thorough EMC testing will examine two things: whether electromagnetic emissions radiated from a device affect other equipment and electronics in the area, and whether a device is susceptible to interference from other devices and other electromagnetic disturbances in its operating environment.

Additionally, devices that incorporate radios will have more regulatory requirements because they communicate as well as emit radio frequencies (RF). The result is often additional testing and approvals from spectrum regulators.

Example: FDA Wireless Coexistence Testing
It is useful to review some of the standards that govern EMC and EMI tests. In the medical device area, for example, the applicable standard is IEC 60601 published by the International Electrotechnical Commission. Compliance with IEC60601-1 has become a requirement for commercializing electrical medical equipment in many countries. But some countries have their own specific requirements as well.

In the U.S., the standard doesn’t apply in nursing facilities, which are considered environments providing professional healthcare. Devices typically mandated to use the standard include oxygen concentrators, body-worn nerve and muscle stimulators, beds, sleep apnea monitors, and associated battery chargers prescribed for use at home. In vitro diagnostic devices, such as blood glucose meters, are covered by another standard called IEC 61010.

In addition to the EMC testing specified in the IEC 60601-1-2 standard, there’s additional FDA-mandated testing when radios are incorporated into medical devices.

Often called co-existence testing, these tests evaluate devices in real-world settings to try to determine scenarios for interference and how a device will react. These real-world scenarios include how the device functions in the presence of emissions from cell phones, cordless phones, Bluetooth devices, Wi-Fi, radio-frequency identification (RFID) and other devices in the area.

Based on the intended product environment, other coexistent devices and test levels may vary. For example, a home device might be tested against cell phones, cordless phones, Wi-Fi and common household RFID devices, while a device intended for use in a hospital would check cell phones, monitoring devices, metal detectors, MRIs or walkie-talkies.

In addition to wireless coexistence, the FDA is also concerned about cybersecurity. Manufacturers of medical devices must be prepared to explain how they address security, especially in the context of any radios that have been added. For example, if you add Bluetooth functionality to your device, can any other Bluetooth device pair with it and take control?

Coexistence Testing Standards Do Not Exist
Standards for wireless coexistence testing, such as ANSI C63.27, are still under development. The latest edition of the medical device EMC standard, IEC 60601-1-2 4th, includes a form of coexistence testing involving simulation of actual radios, but this has not taken the place of FDA wireless coexistence testing. An FDA guidance document, published on Aug. 14, 2013, titled Radio Frequency Wireless Technology in Medical Devices—Guidance for Industry and Food and Drug Administration Staff can be a valuable resource when faced with the specter of coexistence testing.

EMC testing for medical devices resembles the processes that run for consumer electronics like cell phones or televisions. But testing can be more specific and stringent in the medical device industry given the serious consequences of device failures. Because the space is different, there are some things you should keep in mind when it comes to EMC verification.

Taking advantage of experts with EMC knowledge can make the development of any device easier. Independent third-party testing groups can function as a second set of eyes to help ensure a product’s safety and performance. Additionally, third-party groups often have experts on hand who know the space, are familiar with regulatory requirements and have experience that may help inform the testing and development of products.

Manufacturers should also consider the ways their product could impact other devices or be affected by incoming EM fields. While it may sound dramatic or even problematic, testing for the worst-case scenario is essential. Is it possible that a malfunction of your device could result in serious consequences, like injury or death? Illustrating you have considered these scenarios and planned against it will go a long way with the regulatory process.

It may sound obvious, but manufacturers should also be prepared to submit EMC testing data. Because standards for coexistence testing are scarce, test data demonstrates that you have done due diligence, thought ahead and tested against multiple scenarios.

In addition to these suggestions, there are several other considerations for manufacturers when transmitters are being incorporated. Be prepared to get modules tested and approved. Depending on the device, radio modules may need review and approval in addition to the device itself. Even changing antennas may be outside the scope of modular approval and such changes must be considered with verification testing. Care should also be taken to ensure modules are installed in a way that conforms to RF exposure requirements.

Consider geography. Frequency bands are not universal. If your device is offered in different countries, you will need to take this into consideration as you test it. Of course, different countries have different regulatory requirements. Global regulatory approvals vary and can often be complex. Requirements in the U.S. differ from those in the EU. Some countries will accept reports or approvals from other areas, some will not.

In addition, devices that communicate are considered to be radios and, as such, fall under the applicable radio testing requirements of your region. Devices that do not communicate, but simply transfer energy, are thought to emit RF energy to perform a task and will not have the same testing requirements.

References
Intertek Group
www.intertek.com

33 Billion Internet Devices by 2020; Four Connected Devices for Every Person in World. Strategy Analytics. October 14, 2014. https://www.strategyanalytics.com/default.aspx?mod=pressreleaseviewer&a0=5609. Accessed 2/25/15